1. Field of the invention
The invention relates to a mechanical rotary drive, preferably to a gear reduction drive, particularly for industrial robots, for example a manipulator arm rotary drive, comprising a driving side and a power take-off side, a drive shaft and at least two gears, preferably reduction gears, situated on the drive shaft and braced against one another.
2. Description of the prior art
Given industrial robots, manipulators and the like, there is a striving to be able to reach working points in as large as possible a spatial region proceeding from the location of the industrial robot or, respectively, of the manipulator. Particularly given multi-axis, for example 6-axis manipulators, it is also required that operations be carried out at workpieces which comprise an undercut shape with reference to the location of the manipulator, whereby a high, reduplicatable positioning precision is required at the same time. A significant problem in achieving the reduplicatable positioning precision required is the play existing in the rotary drives of the manipulator axes, this adding up with the plurality of axes and being carried over via the reach of the manipulator arms.
In a known rotary drive of the species initially cited (cf. German OS No. 31 15 061), the gears, in order to achieve an optimally play-free reduction of speed, are torsionally elastically connected at the driving side via the drive shaft and, at the power take-off side, are directly connected to the manipulator arm which can be placed in rotational motion via the gearing, this manipulator arm being executed torsionally stiff so that a torsionally stiff coupling of the reduction gearing derives overall at the power take-off side. The torsionally elastic coupling of the gears at the driving side of the rotary drive involves the disadvantage that, particularly given single-sided drive of the rotary drive, irregularities of motion occur dependent on the rotational sense which lead to undesirably great fluctuations with respect to the positioning precision. Although this disadvantage can be countered in that the initiation of torque is centrally provided on the drive shaft, this leads to solutions that are relatively involved structurally, particularly in an industrial robot, and is also disadvantageous with respect to service-friendliness. In order to nonetheless provide a single-sided drive of the drive shaft, the drive shaft must therefore be fashioned in a special way in order to establish an effective torsion angle with respect to the reduction gears which is respectively the same in both rotational senses.